Color detection typically involves filtering light through colored filters (e.g., red, green, and blue filters) and detecting the filtered light to generate color-specific intensity information. Color detection is used in color printers to monitor ink levels in the color ink cartridges. In one implementation, a blue light emitting diode (LED) is used to illuminate color-specific calibration blocks that are printed on a piece of paper. Light that is reflected off the paper is filtered by color-specific filters, detected, and then translated to color-specific intensity values. The color-specific intensity values are then compared to expected color-specific intensity values to determine ink levels in the color ink cartridges. If the printed color of one of the color-specific calibration blocks (e.g., a red calibration block) is determined to be lighter than the expected color, it is likely that the corresponding ink supply (e.g., the red ink cartridge) is low.
Some printers also use optical navigation systems that rely on image correlation to track the position of paper or images relative to the printer. These optical navigation systems collect grayscale image information and correlate features included in the grayscale image information to track position changes. While grayscale image information provides a measure of light intensity, it does not include a color component.
Both color detection and optical navigation are useful features in color printers, however, the systems required to provide these features add complexity and cost to printer systems.